The present invention relates to a serial interface technique for a computer, particularly a technique for making the conventional external memory device of the ATA standard accessible with a command of the USB standard.
A floppy disk drive, a hard disk drive, etc. based on the ATA (AT Attachment) standard are known as conventional external memory devices. These memory devices pose the problem that they easily succumb to an external magnetism and the recorded data are liable to be lost. Also, these memory devices encounter the problem that they cannot be used for a portable terminal such as the PDA (Personal Data Assistance) operated by battery due to a large power consumption.
In order to solve these problems, a technique finds practical applications for recording and reproducing data by handling a memory card using a non-volatile memory such as a flash memory in the same way as the magnetic disk drive.
The conventional external memory device, which operates through a SCSI (Small Computer Serial Interface) constituting a parallel interface, has many pins for a connector. The connector is thus increased in size thereby making it difficult to secure the arrangement location of the connectors of the terminal and the external memory device.
It is considered to solve this problem by sending a command in a serial form from a computer, and processing the command by converting it into a parallel form within the external device. For example, a command based on SCSI is transmitted in a serial form and converted into a parallel form in the external memory device. However, in this case, the computer must process the command in a method different from the existing ones. The solution, therefore, is not practical.
On the other hand, a serial interface of the USB (Universal Serial Bus) standard has recently been proposed. A computer having an input/output port conforming with this standard is also in practical use. By using this standard input/output, data can be stored in and read from an external memory device at high speed. Therefore, data transmission and receipt to and from these cards using USB is expected. Since the command system and the protocol are quite different between USB and SCSI, however, the problem encountered is that the external memory device conforming with the SCSI constituting the conventional hardware and software resources cannot be used.
Also, there is another problem that the supplier of the external memory device must provide two types of system including SCSI and USB.
The above problem is not limited to the external memory device, and a similar problem arises when the communication is to be established between a computer and peripheral equipment thereof.